Revert of Web Animations API: Load resources referenced in element.animate() (https://codereview.chromium.org/196573030/)

Reason for revert:
Causing assertion failure in ChromeOS browser_tests.
https://code.google.com/p/chromium/issues/detail?id=353962

Original issue's description:
> Web Animations API: Load resources referenced in element.animate()
> 
> This patch fixes a bug where resources in element.animate() calls were
> not being fetched. This resulted in StylePendingImages leaking out of
> the style resolving stage and into rendering which causes a crash.
> 
> This patch fixes the bug by ensuring StylePendingImages introduced in
> applyAnimatedProperties() will be resolved as non-pending StyleImages
> through an additional call to loadPendingResources().
> This patch also modifies AnimatableImage to be a wrapper of CSSValues
> instead of StyleImages in order to follow the same resource caching
> logic as typical CSS image values.
> This patch also updates EffectInput::convert() to pass the document's
> StyleSheetContents to MutableStylePropertySet::setProperty() so that
> relative URLs are correctly resolved to absolute URLs.
> 
> BUG=353385
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169424

TBR=dstockwell@chromium.org,esprehn@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=353385

Review URL: https://codereview.chromium.org/203413008

git-svn-id: svn://svn.chromium.org/blink/trunk@169539 bbb929c8-8fbe-4397-9dbb-9b2b20218538